DS_USB_RS485_CABLES Datasheet, PDF (9/16 Pages) List of Unclassifed Manufacturers – 2 Cable Part Numbers

Document Reference No.: FT_000117
USB TO RS485 SERIAL CONVERTER CABLE Datasheet
Version 1.4
Clearance No.: FTDI #75
Parameter Description
Minimum Typical Maximum Units
Conditions
Receiver Input
Common-mode input
VCM
-7
voltage range
+12
V
IN
Input Current
1.0
–0.8
VIN = +12V
mA
VIN = –7V
VTH
DIfferential Threshold
Voltage,VTH
-0.2
+0.2
V
VIHYST Input Hysteresis
20
mV
RIN
Input Resistance, RIN
12
15
kΩ
Transmitter Output
DIfferential Output Voltage,
VOD
1.5
dVOD
5
V
With RL = 54Ω. CL = 50pF *
Table 5.3 USB-RS485-WE I/O Pin Characteristics
* - The 54 ohms is the equivalent of two 120 ohm termination resistors placed on each side of the
transmission line and the input impedance of 32 receivers on the line.
Description
Conditions
ESD HBM
RS-485 Inputs and
Outputs
EN61000-4-2ContactDischarge
RS-485 Inputs and
Outputs
EN61000-4-2AirGapDischarge
RS-485 Inputs and
Outputs
Table 5.4 USB-RS485-WE ESD Tolerance
Minimum
Typical
±15 kV
±8 kV
±15 kV
Maximum
5.4 Local Echo
RS485 systems often have local echo enabled. This means any data transmitted by a device is echoed
back to itself.
The USB-RS485-WE cable allows for local echo to be enabled/disabled by changing a bit in the FT232R
EEPROM. If CBUS4 in the EEPROM is set for “PWRON#” local echo is enabled. If CBUS4 in the EEPROM is
set for “TXDEN” local echo is disabled.
Users can set this with MPROG from www.ftdichip.com
The default for the local echo is disabled (CBUS4 set for “TXDEN).
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